Polymers for drilling and reservoir fluids and their use

Abstract

Aqueous drilling and reservoir fluids are provided comprising polymers with shale and clay inhibition characteristics. These polymers are dissolved in the fluid and are formed from 50 to 100 mo % monomers of formula (I), wherein R 1 is selected from H and C 1 to C 4 alkyl groups; R 2 is selected from C 1 to C 4 alkyl groups, --C(CH 3 ) 2 CH 2 COCH 3 , --CH═CH 2 and --C(CH 3 )═CH 2 . R 3 is selected from H, C 1 to C 4 alkyl groups, CH 2 ═CH-- and CH 2 ═C(CH 3 )--; wherein when R 3 is H or C 1 to C 4 alkyl then R 1 is H and R 2 is --CH═CH 2 or --C(CH 3 )═CH 2 and when R 2 is --C(CH 3 ) 2 CH 2 COCH 3 then R 1 is H; 0 to 50 mol % other ethylenically unsaturated non-ionic monomers and 0 to 20 mol % ionic ethylenically unsaturated monomers and the polymer has a molecular weight of below 1 million.

I claim: 
     
       1. A process of drilling a wellbore in shale-containing rock in which material is removed from the rock and flushed by an aqueous drilling fluid to the surface of the wellbore, in which the aqueous drilling fluid contains a dissolved polymer formed from ethylenically unsaturated monomer or monomer blend, characterized in that the monomer or monomer blend consists essentially of (a) from 50 to 100 mol % monomers of the formula (I) ##STR5##  wherein R 1  is selected from H and C 1  to C 3  alkyl groups R 2  is selected from C 1  to C 3  alkyl groups, --C(CH 3 ) 2  CH 2  COCH 3 , --CH═CH 2  and --C(CH 3 )═CH 2     R 3  is selected from H, C 1  to C 3  alkyl groups, --CH═CH 2  and --CH 2  ═C(CH 3 )-- wherein when R 3  is H or C 1  to C 3  alkyl groups, then R 1  is H and R 2  is --CH═CH 2  or --C(CH 3 )═CH 2     and when R 2  is --C(CH 3 ) 2  CH 2  COCH 3  the R 1  is H       (b) 0 to 50 mol % other ethylenically unsaturated non-ionic monomers selected from the group consisting of acrylamide, methacrylamide, vinyl acetate and hydroxy-ethyl acrylate and wherein the monomer or monomer blend contains substantially no ionic ethylenically unsaturated monomers and the polymer has a weight average molecular weight of 200,000 or less.     
     
     
       2. A process according to claim 1 wherein the monomers of formula (I) are selected from C 1  to C 3  alkyl and dialkyl (meth)acrylamides, N-vinyl formamide, N-vinyl acetamide and diacetone acrylamide. 
     
     
       3. A process according to claim 1 wherein the monomers of formula (1) are selected from N,N-dimethyl acrylamide and N-vinyl formamide. 
     
     
       4. A process according to claim 1 in which the other nonionic monomers comprise acrylamide. 
     
     
       5. A process according to claim 1 in which the monomer blend comprises at least 70% monomers of formula (1). 
     
     
       6. A process according to claim 1 in which the polymer is dissolved in an amount of up to 3% by weight of fluid.